INVESTIGATION OF OCULAR ARTEFACTS IN THE HUMAN EEG AND THEIR REMOVAL BY A MICROPROCESSOR-BASED INSTRUMENT

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Abstract

The Electroencephalogram (EEG) is widely used in clinical
and psychological situations, but it is often seriously
obscured by ocular artefacts (OAs) resulting from
movements in the ocular system (eyeball, eyelids etc). 'The
work described in this thesis is concerned with the
problems of OAs in the human EEG, their removal both
off-line and on-line, and the design and development of an
on-line OA removal system, together with a critical review
of the literature on the subject.
The work of Jervis and his co-workers was extended to
further study OAs, to obtain improved measures of the
effectiveness of OA removal, and to find the most
effective model for removing OA on-line. A number of
criteria were devised to compare the performance of
several models, including a more reliable pictorial
method. It was found unnecessary to use the vertical and
horizontal EOGs for both eyes (ie. four EOGs) in a
removal model, as previously reported. This was shown to
be due to strong correlation between the EOGs.
It was shown that the assumption of uncorrelated error
terms, implicit in present removal models, is invalid. To
remedy this, the error terms were modelled as an
autoregressive series.
New on-line removal algorithms based on numerically stable
factorization algorithms were developed. Compared to the
present on-line methods the algorithms are superior,
requiring no subjective manual adjustments, or the
co-operation of subjects which cannot always be
guarranteed. The algorithms were shown to give similar
results to their off-line equivalents. A simpler
algorithm based on the present on-line method is also
proposed as an alternative, but may lead to a reduced
performance.
An important part of this research lay in the application
of the results to the design and development of a new
automatic OA removal system utilizing the algorithms
described above.

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All items in PEARL are protected by copyright law.
Author manuscripts deposited to comply with open access mandates are made available in accordance with
publisher policies. Please cite only the published version using the details provided on the item record or document.
In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be
sought from the publisher or author.